1. Field of the Invention
This invention relates to a jetting nozzle for production of a high velocity fluid jet.
2. Description of Related Art
The energy in a fluid jet is dependent upon a velocity difference across the jetting nozzle and the flow through the jetting nozzle. Thus, for a given energy jet, a high pressure difference across the jetting nozzle requires a small exit diameter from the nozzle. Once the jet has emerged it spreads out as it entrains the surrounding fluid and since momentum is approximately conserved the jet slows down. The effective range of any fluid jet can be expressed in terms of a number of jet diameters. Thus, for a high energy, high velocity jet, because the jet diameter is small the effective range is also small.
When the fluid of the jet is similar to the surrounding fluid the jet enlarges at an angle of divergence which is characteristic for the fluid. However, when the fluids are dissimilar and the velocity high, the jet enlarges more rapidly and starts to disintegrate at a much shorter distance from the nozzle exit. At very high velocities the jet may disintegrate immediately on, leaving the nozzle exit.
High velocity liquid jets are used, for example, in air or liquid environments for cutting soil in, for example dredging and excavation operations using typical pressures of from 0.3 to 3 MPa and jet diameters of from 8-40 mm. High velocity jets are also used in an air environment for cutting and moving materials for example in monitor mining of minerals such as tin or china clay and for clearing and cooling the stopes in gold mines and the like. For such operations the generating pressures are typically from 3-15 MPa and the jet diameter is from 5-10 mm. In either case the jet does not carry sufficiently far before it disintegrates and the jet must be held much closer to the surface on which it is operating than is practicable.
High velocity jets at typical generating pressures from 10-100 MPa with jet diameters of from 0.5-5 mm are also used for cutting materials such as steel or concrete and for cleaning operations. These jets frequently contain an abrasive. For such operations the effective range of jet is critical.
For all these operations it is highly desirable to provide a jetting nozzle which allows production of a high velocity fluid jet having a greater effective range than conventional jetting nozzles.